/*!
    \file    readme.txt
    \brief   Description of the USB CDC_ACM demo

    \version 2025-08-08, V1.3.0, firmware for GD32E51x
*/

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*/

  This example is based on the GD32E513Z-EVAL-V1.0 board.

  This DEMO is to read data from and write data to USB devices using the CDC protocol. 

  It makes the USB device look like a serial port (NO serial cable connectors: You can see the
data transferred to and from via USB instead of USB-to-USART bridge connection).

  This example loops back the contents of a text file over USB port. To run the example, type 
a message by using the PC's keyboard. Any data that shows in HyperTerminal is received from 
the device.

  The device supports double buffer mode to improve transfer performance, which can be 
configured by modifying the USBD_DOUBLE_BUFFER_ENABLE macro in the usbd_conf.h file.

  - OUT transfers (receive the data from the PC to GD32):
When a packet is received from the PC on the OUT pipe (EP3),by calling cdc_acm_data_receive( )
It will be stored in the usb_data_buffer[]. 
 
  - IN transfers (to send the data received from the GD32 to the PC):
When a packet is sent from the GD32 on the IN pipe (EP1), by calling cdc_acm_data_send(), put the
data into the usb_data_buffer[] buffer for sending data to the host.

  Note 1: When the USBD_DOUBLE_BUFFER_ENABLE macro is enabled, it is recommended to increase 
USB_CDC_RX_LEN to at least twice the maximum packet size to ensure optimal double-buffering performance.

  Note 2: When USB_CDC_RX_LEN is set to n times the maximum packet size (n > 1), the device will only send 
data back to the host after receiving data of length USB_CDC_RX_LEN, or when the length of the received data 
in a single transfer is not an integer multiple of the maximum packet size.
